The OVERALL OBJECTIVE of the proposed research is to improve the long term performance of porcelain-fused-to-metal (PFM) dental restorations by determining the fatigue failure parameters which characterize delayed failure for dental porcelains and by producing new alloys with superior porcelain adherence and thermal compatibility properties. Delayed failure results from growth of flaws to spontaneous catastrophic failure. This research will provide the capability of predicting the length of service of PFM restorations. The success of PFM restorations is very dependent upon a strong porcelain-alloy bond and thermal compatibility. The specific aims are: (1) to develop lifetime prediction curves from dynamic loading of porcelain in simulated oral conditions, (2) to determine if cyclic fatigue has a unique strength degradation compared to non-cyclic fatigue of porcelains and will determine whether an endurance stress limit exists in the porcelains, (3) to compare the predicted lifetimes of porcelain disks to the predicted lifetimes of PFM disks, (4) to produce superior Ni-Cr, Co-Cr,l and Fe-Cr PFM alloys from alloys that have been shown to have very good oxide-metal adherence values, (5) to produce superior palladium-silver alloys from alloys that have been shown not to discolor dental porcelain during fusing, (6) to determine PFM lifetimes using the new experimental alloys. The design of the first experiment is to determine the crack growth characteristics exponent, n, for each porcelain from dynamic fatigue. The values of n will indicate the relative values of predicted lifetime. The second experiment will compare predicted porcelain lifetimes from theoretically equivalent methods. The third experiment utilizes the information from the two previous experiments in determining if the fatigue of PFM disks is simply an extension of porcelain fatigue or whether PFM fatigue is unique in fatigue behavior. The fourth and fifth experiments pursue the development of superior alloys which will encompass adjusting and controlling thermal expansion, melting and casting temperatures, and assessing porcelain adherence. The fatigue properties of PFM disks fabricated from these alloys and the longest porcelain survivor will be carried out to assist in selecting the longest lifetime PFM system.